I used to think that eating disorders were an extreme diet (this was a very long time ago). I thought there were people who didn't diet, people who dieted, and people with eating disorders, all arrayed on a nice little continuum, one blending seamlessly into the next. I've since learned that scholars are still considering this question, albeit in a more academic, less hand-waving sort of way.

Eating disorders are currently classified into three major categories: anorexia nervosa, bulimia nervosa, and eating disorder- not otherwise specified. What we don't know is whether these categories are just humanity's attempts to corral people with eating disorders into three categories, or if these are, in fact, three different eating disorders. Nor do we know if eating disorders are dimensional (ie, they exist along a continuum) or they are taxonic (ie, they have their own category, sort of like humans are a separate species from chimps. We don't have a human-chimp continuum, the behavior of several of my relatives notwithstanding). Perhaps a better analogy would be the difference between a light on a dimmer switch (dimensional model) and a light with an on/off switch (taxonic model). The methods for determining the difference between these use a lot of advanced mathematical models and some really fancy words--I'm not especially concerned in understanding precisely how the determination is made. Rather, I intend to look at whether we can make a distinction, and what that distinction is.

Like many new ideas in science, there is evidence in favor of both views. So let's start with a brief review of the evidence.

Eating disorders are dimensional

Thus far, one study has evidence that restricting anorexia exists along a continuum with "normal eating," although this study also found that bulimia and binge eating disorder do not exist along a continuum (Gleavesetal, 2000a). Perhaps one of the reason why restricting anorexia didn't appear quantitatively different from "normal eating" has to do with the prevalence of dieting behavior, which is more common than not in the college students surveyed in the study. In general, dieters have higher scores on the restraint/weight subsection of the EDI-2, but have similar psychopathology scores as non-dieters (Lowe etal, 1996), which really helps muddy the waters.

Interestingly, the Gleaves study found that the binge/purge subtype of anorexia was much closer to bulimia nervosa than the restricting subtype of anorexia, indicating that binge eating and purging is, in fact, taxometric, whereas restrictive behaviors are more dimensional.

When looking at nonbehavioral eating disorder symptoms (such as fear of fatness, obsession with food/calories), researchers failed to find any sort of eating disordered category, which would indicate that yes, indeed, eating disorders exist along a continuum (Tylka and Subich, 2003). A more recent study, building on this one, found that although eating disordered thoughts are common among people without clinical eating disorders, eating disordered behaviors are rather uncommon (Miller, Vaillancourt, and Hanna, 2009), which has implications on what, precisely, is measured on future studies.

Eating disorders are taxometric

The evidence for both binge eating disorder and bulimia nervosa seem to indicate that these disorders exist as their own categories; that is, either you have them or you don't (Lowe etal, 1996, Gleavesetal, 2000a, Gleavesetal, 2000b). Of course, a diagnosis is rarely as simple as one of those notes you likely received in sixth grade that said "Do you like me? Check yes or no."* There are lots of issues still to be worked out, not the least of which is where do we draw the line?

Perhaps one of the most interesting studies found a middle of the road for this discussion: some eating disorder symptoms existed on a continuum, and some, such as binge eating, fear of fatness/compensatory behaviors, and drive for extreme thinness, did not (Williamson etal, 2003).

Conclusion

At this point, the only consensus on the issue of eating disorder taxometry is the need for more research. Preliminary evidence suggests that bulimia and binge eating disorders are discrete symptoms; the evidence is less suggestive for restrictive anorexia. That being said, eating disordered thoughts are quite common, even if the behaviors are not, which could have significant implications on what is measured and studied in the future.

With the upcoming (and much-heralded) publication of the DSM-V in several years, these seemingly esoteric ideas could have a large impact on how we diagnose, treat, and prevent eating disorders.

Coming tomorrow: Classifying eating disorders, part two (What's temperament got to do with it?)

11 comments:

This post really interested me, as I've read a lot about the transdiagnostic model (Fairburn et al) and never really bought it. I found it too generalised and over simplistic. The destinct differences between some of the ED's make this model too simplistic for my liking.

Despite many years of severe bulimia, Ironically in my heart I would say I was always about the restricting. I didn't want to eat anything, anything at all, and the cycle of b/p seems so close to that unrealistic aim. By aiming for zero calories ingested, I ended up in that repeat cycle. As soon as I realised what was triggering my binges I slammed straight back into restrictive anorexia, and am not convinced that there is a subsection of bulimics who when presented with the facts about purging as a form of weight control, are not at risk of swapping tactics.

BUT that said, I've noticed how bulimia itself can be two destinct types also. Those who seek to eat nothing whatsoever, end crash into a binge through hunger, and those who do it as a secret adjunct to meals and snacks. I have a friend who has a completely normal life, aside from the several times a week she buys a weeks shopping and eats it in one sitting, the throws up, aside from that, her life is picture book idylic. At the height of my BN I was practically a recluse, spending £60 a day on food in a never ending cycle. It's so strange to me that she could eat a normal meal, and then later on in the week binge, just because.

I think anorexia is as distinct on its own as bulimia and binge-eating seem to be.

Do they consider the research that distinguishes those with anorexia so far as how the brain perceives reward, for example? A restricter without an anorexia diagnosis may, indeed, have many obsessive thoughts and body-image issues, but do they fundamentally and neurologically respond to food like the healthy controls or like the even-weight-restored anorexics?

Is the brain processing reward at the site of food or fear? How do the brains of those on a dimensional model process emotions; approach tasks; do they express co-morbid pathology; do they have family history of an eating disorder, autism or other mental disorders, such as anxiety, depression or OCD?

Practically everyone in modern Western culture is a "restricter," but the statistics have remained constant for the number of those with anorexia (something like 1-3 percent of the population?)

That seems indicative, to me, of a classification of its own ... one we still only vaguely understand and which eludes a standard, effective treatment protocol.

I think those of us with eating disorders now and in the past 25 years are challenged by them in an era of discovery ... and the next generation will benefit from the questions (and, I hope, eventual answers) about the nature of this terrible illness.

What if both? What if neither? What if there's a fence you can climb and straddle and then (whoops) you've fallen over? Because I used to restrict. But then was given hormones which caused bingeing that I was unprepared for, which triggered 2 years of intense bulimia, with fasts scattered throughout. But just recently, that fence? I've sort of climbed it and sat on the top looking over on both sides (anorexia, bulimia) for several months, alternating for weeks at a time. Then I fell, and I would say by all DSM-IV standards, other than I haven't had time to lose the weight or period yet, I am on the anorexic side again. I am no longer bulimic anymore.

But what if there IS both a continuum AND a taxonomy? Somewhat like how light can be a particle and a wave, type of thing.

I'm awful with words. What I'm trying to say is, what if it's not that easy (to categorize). What if there's just characteristics, rather than "eating disorders," but just Eating Disorder. You throw up or you starve or you binge or you take diet pills or laxatives, you just do some more than others.

It's just doctors want so bad to classify everything, and I totally understand. My favorite pastime (I do not joke you) is to find jumbled beads or similar items, and sort by color and type. So I absolutely understand the even more intense urge doctors have to classify and sort disorders into their proper categories. But I don't think it's that easy. Not with this. I don't think it may be possible.

My idea is it's more of a pond of something (like water) with varying (depths? qualities? colors?) conditions, and you may be at somewhere in the pond or you may be somewhere else. It's not square, it's more round. It's not as easy to break down, the disorders blend together. The categories blend.

I'm wondering which one leaves more hope for recovery. I mean, people can recover regardless of whether one's particular illness is dimensional or taxonomical. But I wonder what approach is most helpful to someone in treatment. I'm currently in treatment and am hoping that there's an "off" switch that I can find if I do everything I'm told to do in treatment. I don't think it works that way for me, though, simply because I've slid around my own personal dimensional scale for years. Is the goal to rid myself of eating disordered thoughts? behavior? Is the goal to be like the majority of western women without an ED--often preoccupied with food and body but not acting out? Is the goal to lower my number on the spectrum or to switch it off altogether? Would the goal be different if I were clinically anorexic instead of diagnosed with ED-NOS (binge/restrict)?

To be honest, I'm surprised that the findings indicated that bulimics and binge eaters leaned toward a taxonomical model and anorexics toward dimensional. The people I know who are diagnosed with anorexia seem to be on some other sort of model that, even in my deepest restriction, seemed somehow different than what I was doing. I suppose the idea is that restricting falls onto a sliding scale (I didn't realize I was restricting because I was eating, just not nearly enough), whereas purging is rather distinct?

Thanks for sharing your history--it does make a lot of sense. There is just so much we don't know.

M,

I shall answer your question (at least somewhat) in the part two post I do later today.

Mad Bird,

I definitely understand the need to categorize things, and I do understand how certain aspects of EDs can be dimensional and certain aspects might be distinct categories. And like you said with the beads, it might depend on what criteria are ultimately used.

And I organize my closet by color, and I was rather stymied by multi-colored shirts. So I gave them their own little section, which strikes me a bit as to what the solution might be for EDs.

Woman,

I don't really have an answer for you, but you raise some really good questions I think should be addressed no matter what. There are definitely problems in diagnosing eating disorders, because people with EDNOS don't usually differ clinically from those with other EDs. Again, stay tuned because I will be looking at that just a little bit later today.

I have heard a number of psychiatrists suggest that the temperament traits that underpin EDs lie on a continuum. At one end there is the individual prone to impulsive behaviours, including binge eating and self harming. Some of such individuals also have borderline personality disorder. At the opposite end of the continuum is the restricting anorexic, who is over-controlled and may display autistic thinking, or be diagnosed with an autism spectrum disorder.

I fit the profile of the over-controlled individual, with a history of restricting anorexia nervosa and with autistic traits. I know a number of lovely people at the opposite end of the continuum who are very, very different to the way that I am. The type of treatment that may benefit them probably wouldn't benefit me whatsoever.

Therefore, I think that people with EDs may lie on a spectrum, with some folks in the middle of that spectrum who are difficult to categorise. The eating and co-morbid behaviours of people at either end of the continuum (or maybe it's a normal distribution?) may be very different and have different personal meanings to the individual.

I simply don't believe that there's an effective 'one size fits all' approach to treatment of EDs as a whole, or even the current sub-categories in DSM IV. EDs always have something of an individual, distinct, personal meaning to every sufferer.

I wonder about some of the points that Cathy raised too. I had EDNOS in my teens and fit the undercontrolled personality traits more typical of someone with bulimia, but during my early 20s my disorder became purely restricting anorexia and my personality changed to match. I stopped self harming and bingeing, started studying all the time (I could never sit still for long enough in my teens to revise), became well organised and punctual (I used to always be late for everything), found that I didn't want support or comfort when bad things happened (I had previously found it impossible to cope with anything difficult on my own)...it was like I was a totally different person. And I'm different again now I'm in recovery. Hopefully somewhere in the middle of those extremes. I've also frequently wondered if there is a quantitative difference between people with anorexia who are predominantly obsessed with weight and shape and those whose behaviours are perpetuated by other fears. For me, losing weight made me feel safe in the same way that my OCD rituals did, but I never had the thought processes related to feeling 'fat' and wanting to lose weight for appearance sake. I know those are symptoms not causes, but there seems to be a huge variation in the way that anorexia can present, even before you take bulimia, BED and EDNOS into consideration.

Okay, I get the confusion now. I don't think I was clear about what was being considered continuum/categorical. I totally understand that the different eating disorder diagnoses and symptoms can exist along a continuum- that I agree with. It seems as much a mix-n-match game as anything else. There is some research to suggest that personality and temperament more accurately subtype eating disorders rather than symptoms.

HOWEVER, the studies that I was talking about were looking at whether eating disorders were just an extreme version of unhealthy eating. If you take Ellyn Satter's definition of normal eating as one end of the continuum, then are eating disorders (of any type) on the other end of that continuum? Or are they categorically different from anything on the eating continuum?

"There are gophers and there are chipmunks but there are no gophmunks." In other words, gophers and chipmunks both represent taxa - naturally occurring qualitatively distinct groups and do not lie upon a single gopher-chipmunk continuum.

In the studies I blogged about, the gopher-chipmunk continuum would be normal eating and eating disorders, as opposed to a continuum of anorexia to bulimia to binge eating.

Very interesting! I have to say that I don't think eating disorders are anything like an extreme version of unhealthy eating. I think there is so much brain wiring involved with developing an eating disorder and I think only a small handful of people would progress from a diet to an eating disorder. I think it's easy for researchers to label bulimia as taxometric because they say, "either you binge and purge, or you don't." Restricting is sort of a fuzzy category. Lots of women restrict, but they are eons away from having anorexia, in that their brains are just not wired that way. I eat more than 90% of the women I know, yet I would still classify my thoughts and some behaviors (with food, money, etc) as "anorexic." I think it's hard for researchers to figure out when the line is crossed with restricting. It can seem like one day, you're dabbling with calories, and the next day you're obsessed. I look forward to part two :)

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I'm a science writer, a jewelry design artist, a bookworm, a complete geek, and mom to a wonderful kitty. I am also recovering from a decade-plus battle with anorexia nervosa. I believe that complete recovery is possible, and that the first step along that path is full nutrition.